Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example, U.S. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a photoconductive insulating element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well-known in the art, can then be employed to produce a permanent record of the charge image.
Various types of photoconductive insulating elements are known for use in electrophotographic imaging processes. In many conventional elements, the active components of the photoconductive insulating composition are contained in a single layer composition. This layer is coated on a suitable electrically-conductive support or on a non-conductive support that has been overcoated with an electrically-conductive layer.
Among the many different kinds of photoconductive compositions which may be employed in typical single-active-layer photoconductive elements are inorganic photoconductive materials such as vacuum-deposited selenium, particulate zinc oxide dispersed in a polymeric binder, homogeneous organic photoconductive compositions composed of an organic photoconductor solubilized in a polymeric binder, and the like.
Other especially useful photoconductive insulating compositions which may be employed in a single-active-layer photoconductive element are the high-speed heterogeneous or aggregate photoconductive compositions described in Light, U.S. Pat. No. 3,615,414 issued Oct. 26, 1971 and Gramza et al, U.S. Pat. No. 3,732,180 issued May 8, 1973. These aggregate-containing photoconductive compositions have a continuous electrically-insulating polymer phase containing a finely-divided, particulate, co-crystalline complex of (i) at least one pyrylium-type dye salt and (ii) at least one polymer having an alkylidene diarylene group in a recurring unit.
In addition to the various single-active-layer photoconductive insulating elements, such as those described above, various multi-active photoconductive insulating elements, that is, elements having more than one active layer, are also well known and, in general, are capable of providing superior performance. In such multi-active elements, at least one of the layers is designed primarily for the photogeneration of charge carriers and at least one other layer is designed primarily for the transportation of these charge carriers.
A particularly important class of charge-generating agents for use in multi-active photoconductive insulating elements is the class of perylene compounds. Thus, it is known in the prior art that the perylenes are capable of providing exceptional performance and many proposals have been made heretofore for the use of perylenes of widely varying structure. Most typically, the perylenes which are described as being especially useful in electrophotography are diimides characterized by the generic formula: ##STR1##
Representative examples of the many patents describing the use of perylenes of the above formula in multi-active photoconductive insulating elements include the following:
U.S. Pat. No. 3,871,882 to Wiedemann, issued Mar. 18, 1975, in which R is hydrogen, alkyl, aryl, aralkyl, a heterocyclic group or --NHR.sup.1 in which R.sup.1 is phenyl or benzoyl.
U.S. Pat. No. 3,904,407 to Regensburger et al, issued Sept. 9, 1975, in which R is alkyl, aryl, alkylaryl, alkoxyl, halogen or a heterocyclic group.
U.S. Pat. No. 4,156,757 to Graser et al, issued May 29, 1979, in which R is hydrogen, alkyl, oxaalkyl, cycloalkyl, alkaryl, aryl, halogen, nitro, amino or hydroxyalkyl.
Japanese Patent Publication No. 36849/55 assigned to Ricoh Company Ltd., published Mar. 14, 1980, in which R is hydrogen, aryl, alkyl, alkylaryl, halogen or a heterocyclic group.
U.S. Pat. No. 4,419,427 to Graser et al, issued Dec. 6, 1983, in which R is a 2,6-dichlorophenyl group.
U.S. Pat. No. 4,429,029 to Hoffman et al, issued Jan. 31, 1984, in which R is hydrogen, alkyl, aralkyl, aryl or alkylaryl and the aromatic skeleton is halogen-substituted to an extent of at least 45 percent.
U.S. Pat. No. 4,514,482 to Loutfy et al, issued Apr. 30, 1985, in which R is a trialkyl- or triaryl-substituted phenyl group.
U.S. Pat. No. 4,517,270 to Graser et al, issued May 14, 1985, in which R is propyl, hydroxypropyl, methoxypropyl or phenethyl.
U.S. Pat. No. 4,578,334 to Borsenberger et al, issued Mar. 25, 1986, in which R is a 2-phenethyl group.
While many different perylenes have been disclosed in the prior art to be useful in multiactive photoconductive insulating elements, they typically lack sensitivity in the far red region of the spectrum, i.e., in the region of from 650 to 700 nm. This is a very serious disadvantage as regards use of the photoconductive elements in devices such as electronic printers in which the exposure devices are typically lasers or light emitting diodes that emit in the far red.
It is toward the objective of overcoming the aforesaid disadvantage of known multi-active photoconductive insulating elements comprising perylenes that the present invention is directed.